Art of dewaxing hydrocarbon oils



Patented Apr. 7, 1936 UNITED STATES PATENT OFFICE John A. Anderson, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application August 27, 1930, Serial No. 478,303

2 Claims. (Cl. 19617) The present invention relates to the separation of wax from hydrocarbon mineral oils, and particularly those waxes which are difficult to separate by the usual pressing operation. The

5 invention is particularly adapted to be employed in connection with the separation of waxes found in the lubricating type of hydrocarbon oil distillates, i. e., those produced by non-cracking distillation of petroleum residuums and containing substantial quantities of wax of properties and molecular weight intermediate those of paraffin wax and petrolatum, known in the art as slop wax.

It has been found that these waxes may be 5 separated from such distillates by taking advantage of the difference between the specific gravity of the wax and the oil. The wax-containing oil is diluted with a suitable diluent miscible with the distillate and of relatively low viscosity, for example naphtha, a small quantity of petrolatumtype wax is added, the diluted oil is chilled, and the wax permitted to settle out of the chilled mixture or separated therefrom by a centrifuging operation. It has been found that in this way a 5 greatly improved separation of the oil and wax and consequent increased yield of lubricating oils can be secured.

In accordance with the present invention, the wax thus separated from the oil is subjected to distillation under conditions characteristic of sub-atmospheric distillation, i. e., vacuum distillation or distillation with steam or other suitable inert gas, and, I have found that the greater portion of the waxes are distilled over and residuum is thereby produced which resembles petrolatum in that a suitable portion of it may be employed to aid the separation of wax from subsequent batches of such wax-containing oils instead of the extraneous petrolatum employed to aid separation of the initial batch. The amount of such wax which is recoverable from the separated waxy materials, ordinarily, more than exceeds the amount necessary to aid the separation of wax from a subsequent similar sized batch of slop wax-containing distillate. Thus, the process is self-sustaining from the standpoint of the supply of petrolatum-type wax required for aiding separation of waxes from the hydrocarbon distillates.

The oil to be treated may be a heavy lubricating distillate out, such as those represented by fractions between and off on a, Mid-Continent crude. Such cuts ordinarily have a viscosity of 75 to 120 sec. Saybolt at 210 F. However,

55 it is to be understood that the invention is not intended to be limited to the treatment of this particular cut, since it is applicable to any uncracked hydrocarbon oil distillate containing substantial quantities of waxy material difficult to separate by a pressing operation, such as slop 5 wax.

The distillation of the separated waxy materials may be carried out below cracking temperatures say below 650 F. and preferably between 520 and 550 F. It is ordinarily preferred to ef- 10 feet this: distillation with steam. When vacuum distillation is employed, it is preferred that the absolute pressure be in the order of 5 to 10 millimeters of mercury, and when steam distillation is employed it is preferred that sufl5 ficient steam be used to provide from one to two volumes of condensed water per volume of distillate taken off. The distillation is carried on until the diluent, (which is ordinarily naphtha), the oil and waxes (largely pressable and sweat- 20 able waxes) other than the petrolatum-type waxes hereinbefore referred to have been distilled off, leaving the petrolatum-type wax in the residue. The residue may then be employed to aid the separation of the slop wax from a sub- 25 sequent batch of wax-containing distillate. If desired, a substantial portion of the oil contained in the separated waxy material may be removed therefrom before the distillation operation is begun. This may be accomplished by diluting the 30 separated waxy material with additional naphtha and settling or centrifuging the diluted material at a low temperature. The re-separated waxy material may then be subjected to the distillation operation already described.

The invention will be more readily understood from the following specific example: A distillate containing slop wax, constituted by the cut between 84% off and 87% off from Mid-Continent crude, having a viscosity of about 90 sec. Saybolt 40 at 210 F., solid between 80 and F. and containing between 7 to 12% of wax of the slop wax type, is diluted with about 70% of naphtha of about 400 F. end point. A small amount, for example, between 1 and 5% of petrolatum wax 45 having a melting point between and F. and containing between 30 and 70% of oil, is added to the diluted distillate. The diluted distillate is now slowly chilled -10 F. and maintained at that temperature for between 60 and 50 80 hours. During this time the wax settles out, leaving a supernatent layer of clear oil amounting to between '70 and 80% of the whole. After removing the naphtha, the oil has a pour point of from 15 to 20 F. If desired, the settled 55 naphtha-free oil can be subjected to the usual refining operations, 1. e., acid treatment and/orclay decolorization treatment.

The settled wax (containing some oil) from the settling operation is then subjected to distillation under conditions characteristic of subatmospheric pressure distillation in the manner already described. The resulting residue, containing a substantial portion of the original petrolatum as well as additional petrolatum-type wax separated from the chilled distillate, is then employed in part to aid the settling or centrifuging of slop wax from a subsequent batch of distillate.

The residue formed during the distillation of the waxes settled from the slop wax-containing distillate ordinarily. comprises about 20% of the total wax settlings and may or may not contain sufficient oil to render it sufficiently fluid to be readily added to a subsequent batch of slop waxcontaining distillate. Ordinarily the oil content of the recovered petrolatum wax may be controlled by the distillation conditions, but in any event sufiicient oil may be added to the separated petrolatum type wax to render is suificiently fluid for easy admixture with the next batch of slop wax-containing distillate to be treated.

Ordinarily, in carrying out the process of separating slop wax from slop wax-containing distillates in connection with the present invention, the petrolatum wax content of the material separated from the chilled distillate tends to build up as the amount separated from the chilled oil along with the slop wax is in excess of the amount necessary to aid the separation of slop wax from a similar batch of such distillate. The amount in excess of that required for treatment of a subsequent batch may be used in other processes or operations or refined as a product.

It will be seen that the process, when carried out in accordance with the present invention, is self-sustaining from the standpoint of the supply of petrolatum-type wax for aiding the separation of slop-wax from the distillate being treated. Under normal conditions it should not be necessary to employ extraneous petrolatum,

aside from that necessary to aid separation of slop wax from the initial batch treated.

In case the slop wax-containing distillate to be treated has? been clayed to color before the settling operation, it is preferable to treat the petrolatum, or petrolatum-type residue, to color before it is added to the distillate to avoid discoloration of the latter. This purification may be effected by filtering it with clay.

Although the present invention has been described in connection with the details of a specific embodiment thereof, it is not intended that such details shall be regarded as limitations upon the scope of the invention, except insofar as included in the accompanying claims.

I claim:

1. A petroleum refining process which comprises adding to a Waxy oil stock a residue from the distillation of a wax mixture, said residue having the property of preventing wax from precipitating from the oil in the form of interlacing crystals, diluting the mixture with an oil miscible liquid of relatively low viscosity, chilling the mixture and mechanically separating sweatable wax with entrained oil and residue from the diluted mixture by mechanical means dependent on the crystal structure of the wax, and distilling oil and wax from the residue under non-cracking conditions whereby the residue has the property when dissolved in the wax-bearing oil of preventing the precipitation of wax in interlacing crystals.

2. The method of preparing a substance for preventing wax from precipitating from oil in the form of interlacing crystals which comprises diluting oil containing slop wax with an oilmiscible fluid of relatively low viscosity, chilling the mixture and separating wax from diluted oil by cold settling, removing the separated wax from the oil and distilling the removed wax under non-cracking conditions to remove diluent, oil and crystalline wax, the residue of the distillation having the property, when dissolved in a wax-bearing oil, of preventing the precipitation of wax in interlacing crystals.

JOHN A. ANDERSON. 

